Many cellular phones and other compact mobile devices use Lithium-ion (Li-Ion) battery chemistries, as this chemistry has desirable energy density and charge/discharge characteristics. However, this type of battery can suffer from certain disadvantages, including a risk of explosion if overcharged. Other disadvantages may include the possibility of damaging the battery if it is charged too quickly, discharged too quickly, or discharged too thoroughly.
Because of the above factors, one typically finds Li-ion batteries and other rechargeable batteries such as nickel-based batteries not as stand-alone cells, but as battery systems including the actual cell(s), along with additional components and circuits designed to protect the battery and its user. The circuitry can disable a battery if the battery voltage falls below a threshold level, to avoid excessive discharge of the battery.
Furthermore, many devices include control mechanisms to enable charging of the battery pack at various levels, depending on the voltage of the battery pack. While these charging mechanisms are designed to prevent damage to the battery, because of the various protection circuitry that may be present within a battery pack, the voltage obtained from the battery pack may not necessarily be indicative of the actual cell voltage, and thus such charging regimes may not operate as intended.